Known in the present state of the art is a method for semiautomatic processing of electro-oculographic signals (cf. Mode. 7310/7102/7402 Operating Manual. Life-Tech. Instruments, Houston, Tex.; Cadwell 5200. Archives of Ophthalmology, 1983, vol. 101, No.3, p.345; Cadwell 7400. Archives of Ophthalmology, 1983, vol. 101, No.4, p.549), consisting in visual stimulation and storing of the input bioelectric (action) potential in the memory of the apparatus, or its taking down by a recorder. According to the method, the measurement results are obtained by extracting the bioelectric potential signal from the memory, displaying it graphically as a curve on a screen, tracing a videomarker along the displayed curve and fixing the bend points of the signal curve, while spurious signals are filtered out by the operator himself.
The method in question involves direct participation of man in recording an electro-oculogram and isolating intelligence electro-oculographic signals from the recorded input signal, as well as requires much time to be spent by the operator.
Another method for automatic processing of electro-oculographic signals is known (cf. "Pulse electro-oculography--a new objective method of clinical electro-oculography" by V. Ya. Eskin and D. I. Kaplunovich, Vestnik oftalmologii, 1983, No. 4, p.6 (in Russian), wherein an electro-oculographic potential is represented as the ratio of the maximum rate of rise of an input signal of action potential to the weighted mean value (or the value measured by some other method) of the maximum angular rate of eyeball rotation.
Such a method is featured by a considerable loss of accuracy of every particular measurement in case of division by the weighted mean value of the maximum angular rate of eyeball rotation. In addition, the result obtained depends upon the angle of eyeball rotation, since the derivative of the input signal is the function of the angle of eyeball rotation. Furthermore, the method involves additional determination of a specific value of the maximum angular rate of eyeball rotation.
One more method for automatic processing of electro-oculographic signals consists in integrating a bioelectric potential drawn from a patient within a preset lapse of time (cf. M. J. Holland, F. Clark. An automatic measuring and recording system for clinical electro-oculography. Ophthal. Res., v.3, p.311-319, 1972).
However, this method also suffers from a badly affected accuracy of results obtained due to long-time erroneous gaze shifting.
Known heretofore is a method for automatic processing of electro-oculographic signals (cf. Jackson S. A. Automated electro-oculography--a microprocessor application example, J. of Medical Eng. & Technology, v.4, No. 6, 1980, p.285-289), consisting in visual stimulation with the aid of a ruler composed of 32 light stimuli whose changing-over should be traced visually by the patient, recording the five values of the action potential signal amplitude, followed by processing said values with a view to selecting any three of them falling within the framework of a preset aperture, averaging said values and normalization to the angle of eyeball rotation to obtain a constant electro-oculographic potential of the eye.
The method under consideration is characterized by:
complicacy of visual stimulation;
necessity of bringing visual stimulation in synchronism with patient's gaze shifting;
susceptibility of the results to various disturbances, such as erroneous gaze shifting, particularly on account of a possibility of selecting three amplitude values through falling within the frame of the aperture but proving to be erroneous (which may be the case with low amplitude values and a large aperture).
A method for automatic processing of electro-oculographic signals (cf. Pantops 500. Mode d'Emploi. Schlumberger Instruments et Systemes) is in fact the one most resemblant to the method of the present invention. This prior-art method resides in subjecting the patient to visual stimulation at a preset angle and within a preset period of time, recording the action potential signal of the patient's eye, amplifying said signal, limiting the spectrum of said action potential signal, measuring the amplitude of the action potential at preselected instants of time, and processing the measurement results to obtain a constant electro-oculographic constant of the eye. The preselected time instants at which the amplitude of the action potential is measured are referred strictly and invariably to the numbers of stimulation cycles from the very beginning of measurements and correspond to the midpoints of the time intervals between each change-over of the visual stimuli. Four amplitude values are fixed, i.e., those corresponding to the gaze at the right, at the centre, at the left and at the centre again. The amplitude values thus obtained are then displayed on a CRT screen and measured manually by the operator. There is assumed as an informational value a difference between the amplitude value corresponding to the gaze at the right and left and that corresponding to the gaze at the centre. A constant electro-oculographic potential results from normalization of the thus-obtained deviation of the amplitude value to the angle of eyeball rotation (or to the sinus thereof).
The method discussed above, however, suffers from the following disadvantages:
low accuracy of results obtained, since the measurement process makes no provision for isolating the intelligence electro-oculographic signals from the whole input signal in which signals caused by nystagmoid eye movements, nictitation, etc. are present;
reliable and trustworthy results are attainable only when complete synchronism of visual stimulation and patient's gaze shifting is provided, which cannot be observed in a majority of cases.